Get relative path of files in sub-folders from the current directory
Solution 1:
The Resolve-Path cmdlet has a -Relative parameter that will return a path relative to the current directory:
Set-Location C:\MyScript
$relativePath = Get-Item Data\Test.txt | Resolve-Path -Relative
Solution 2:
In case the directory doesn't exist, or the base directory should be different from the current working directory, there's a .NET method [IO.Path]::GetRelativePath(String from, String to).